Oscillators are used in various communications devices, including both wired and wireless communication devices. With increasing demand for improved performance in communication devices, including more stringent requirements for signal integrity and modulation specifications, there is also increasing demand for better performance of oscillators, including better phase noise performance. One approach for reducing phase noise in an oscillator is to increase the amount of energy stored in the resonator. However, in conventional oscillator design, the voltage swing (which increases with stored energy) rises with the bias current in the current limiting region, and this voltage swing growth is typically limited by the breakdown voltage of an active device (e.g., transistor) that is directly connected to the resonator.
There is also a trend towards higher frequencies for communication signals, and a trend towards integration of radio frequency (RF) and digital components. These trends tend to favor smaller circuitry operating at lower voltages, particularly as supply voltages are tending to decrease (e.g., to 1V or less). As a result, the energy that can be stored in an oscillator resonator is decreased, leading to worse phase noise.
There is a desire to provide an oscillator that is able to provide improvements in phase noise.